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Re: [Discuss-gnuradio] Question about sampling

From: Dinkar Bhat
Subject: Re: [Discuss-gnuradio] Question about sampling
Date: Thu, 17 Mar 2005 15:28:26 -0500
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)

Thanks for the info. One of my issues is the detection of the pilot frequency
(which is a specific frequency relative to the channel). Now, using FFT on the samples
that I captured using the ADC, I geta  certain frequency resolution (bin size) that is inversely
proportional to the the length of the ADC. But I might miss the pilot and hence I was wondering
if I should sample at much higher rate than 2* max frequency. Even then I might miss
the pilot, and I am wondering what is approach?


cswiger wrote:
On Wed, 16 Mar 2005, Dinkar Bhat wrote:

I joined this group recently and have learnt a lot.

Join the crowd (that are learning a lot)

I had a rather
fundamental question. Suppose I sample the
IF output (say, centered at 40 Mhz) of a tuner/mixer tuned to a ATSC DTV
channel (6Mhz wide), and I want to detect the
pilot frequency which is added to the channel during transmission, would
I have to sample the IF
at much higher than 2*Nyquist fy? The reason I ask is that the pilot

If the IF is bandlimited (say 40 +- 4Mhz) you can sample at a much lower
rate using 'bandpass sampling', use a slower ADC and get fy translation
at the same time. For example, a tuner we use is centered at 36Mhz, our
ADC samples at 64Mhz ( < 2* IF ) but the IF appears to be at 28Mhz
( 32 - ( IF - 32 )).



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